<template>
  <scroll ref='listview'
          class='listview'
          :data='data'
          :listenScroll='listenScroll'
          @scroll='scroll'
          :probeType='probeType'>
    <ul>
      <li v-for='(group, index) in data'
          class='list-group'
          :key='index'
          ref='listGroup'>
        <h2 class='list-group-title'>{{group.title}}</h2>
        <ul>
          <li @click='selectItem(item)'
              v-for='(item, index) in group.items'
              class='list-group-item'
              :key='index'>
            <img class='avatar'
                 v-lazy="item.avatar" />
            <span class='name'>{{item.name}}</span>
          </li>
        </ul>
      </li>
    </ul>
    <div class='list-shortcut'
         @touchstart='onShortcutTouchStart'
         @touchmove.stop.prevent='onShortcutTouchMove'>
      <ul>
        <li v-for='(item, index) in shortcutList'
            class='item'
            :data-index='index'
            :key='index'
            :class='{current: currentIndex===index}'>
          {{item}}
        </li>
      </ul>
    </div>
    <div class='list-fixed'
         v-show='fixedTitle'
         ref='fixed'>
      <h2 class='fixed-title'>{{fixedTitle}}</h2>
    </div>
    <div v-show='!data.length'
         class='loading-container'>
      <loading></loading>
    </div>
  </scroll>
</template>

<script type="text/ecmascript-6">
import Scroll from 'base/scroll/scroll'
import Loading from 'base/loading/loading'
import { getData } from 'common/js/dom'

const TITLE_HEIGHT = 30
const ANCHOR_HEIGHT = 18

export default {
  name: 'Listview',
  created () {
    this.touch = {}
    this.listenScroll = true
    this.listHeight = []
    this.probeType = 3
  },
  data () {
    return {
      scrollY: -1,
      currentIndex: 0,
      diff: 0
    }
  },
  props: {
    data: {
      type: Array,
      default: null
    }
  },
  computed: {
    shortcutList () {
      return this.data.map((group) => {
        return group.title.substr(0, 1)
      })
    },
    fixedTitle () {
      if (this.scrollY > 0) {
        return
      }
      return this.data[this.currentIndex] ? this.data[this.currentIndex].title : ''
    }
  },
  methods: {
    selectItem (item) {
      this.$emit('select', item)
    },
    onShortcutTouchStart (e) { // 右侧点击事件
      let anchorIndex = getData(e.target, 'index')
      let firstTouch = e.touches[0]
      this.touch.y1 = firstTouch.pageY
      this.touch.anchorIndex = anchorIndex
      this._scrollTo(anchorIndex)
    },
    onShortcutTouchMove (e) { // 右侧滑动事件
      let firstTouch = e.touches[0]
      this.touch.y2 = firstTouch.pageY
      let delta = (this.touch.y2 - this.touch.y1) / ANCHOR_HEIGHT | 0 // 向下取整
      let anchorIndex = parseInt(this.touch.anchorIndex) + delta
      this._scrollTo(anchorIndex)
    },
    refresh () {
      this.$refs.listview.refresh()
    },
    scroll (pos) {
      this.scrollY = pos.y
    },
    _scrollTo (index) { // 左侧滚动到相应位置
      if (index < 0) {
        index = 0
      } else if (index > this.listHeight.length - 2) {
        index = this.listHeight.length - 2
      }
      this.scrollY = -this.listHeight[index]
      this.$refs.listview.scrollToElement(this.$refs.listGroup[index], 0)
    },
    _calculateHeight () {
      this.listHeight = []
      const list = this.$refs.listGroup
      let height = 0
      this.listHeight.push(height)
      for (let i = 0; i < list.length; i++) {
        height += list[i].clientHeight
        this.listHeight.push(height) // 获得listgroup区间
      }
    }
  },
  components: {
    Scroll,
    Loading
  },
  watch: {
    data () {
      setTimeout(() => {
        this._calculateHeight()
      }, 20)
    },
    scrollY (newY) {
      // 监听scrollY变化，改变currentIndex值来改变字母样式
      const listHeight = this.listHeight
      // 滚动到顶部，newY>0
      if (newY > 0) {
        this.currentIndex = 0
        return
      }
      // 中间部分滚动
      for (let i = 0; i < listHeight.length - 1; i++) {
        let height1 = listHeight[i]
        let height2 = listHeight[i + 1]
        if (-newY >= height1 && -newY < height2) {
          this.currentIndex = i
          this.diff = height2 + newY // 滚动的距离和任一列表的差值
          return
        }
      }
      // 滚动到底部且-newY大于最后元素的上限
      this.currentIndex = listHeight.length - 2
    },
    diff (newVal) {
      let fixedTop = (newVal > 0 && newVal < TITLE_HEIGHT) ? newVal - TITLE_HEIGHT : 0
      if (this.fixedTop === fixedTop) { // 为了减少dom操作的频率
        return
      }
      this.fixedTop = fixedTop
      this.$refs.fixed.style.transform = `translate3d(0,${fixedTop}px,0)`
    }
  }
}

</script>

<style scoped lang="stylus" rel="stylesheet/stylus">
@import '~common/stylus/variable'
.listview
  position: relative
  width: 100%
  height: 100%
  overflow: hidden
  background: $color-background
  .list-group
    padding-bottom: 30px
    .list-group-title
      height: 30px
      line-height: 30px
      padding-left: 20px
      font-size: $font-size-small
      color: $color-text-l
      background: $color-highlight-background
    .list-group-item
      display: flex
      align-items: center
      padding: 20px 0 0 30px
      .avatar
        width: 50px
        height: 50px
        border-radius: 50%
      .name
        margin-left: 20px
        color: $color-text-l
        font-size: $font-size-medium
  .list-shortcut
    position: absolute
    z-index: 30
    right: 0
    top: 50%
    transform: translateY(-50%)
    width: 20px
    padding: 20px 0
    border-radius: 10px
    text-align: center
    background: $color-background-d
    font-family: Helvetica
    .item
      padding: 3px
      line-height: 1
      color: $color-text-l
      font-size: $font-size-small
      &.current
        color: $color-theme
  .list-fixed
    position: absolute
    top: 0
    left: 0
    width: 100%
    .fixed-title
      height: 30px
      line-height: 30px
      padding-left: 20px
      font-size: $font-size-small
      color: $color-text-l
      background: $color-highlight-background
  .loading-container
    position: absolute
    width: 100%
    top: 50%
    transform: translateY(-50%)
</style>
